80 DISSECTION OF THE BRAIN. 



g. The Pons Varolii is the large band of trans- 

 verse fibres lying back of the crura cerebri. It con- 

 sists of transverse commissural fibres connecting the 

 two sides of the cerebellum. Followed up toward 

 the dorsal side it will be seen to pass into the cere- 

 bellum on each siae, forming the middle peduncles of 

 the cerebellum. 



h. Corpus Trapezoideum, a band of similar trans- 

 verse fibres lying posterior to the pons, and inter- 

 rupted in the mid-line by the anterior pyramids. 



i. The Anterior Pyramids, the two bands of 

 longitudinal fibres lying on the ventral surface of the 

 medulla and ending (apparently) anteriorly in the 

 pons. The anterior median fissure also ends at the 

 pons. 



3. The Roots of the Twelve Cranial Nerves. 



a. The Olfactor\ or I. cranial nerves arise from 

 the under side of the olfactory lobes; most probably 

 they were torn off in removing the brain. 



b. The Optic or II. cranial nerves arise from the 

 anterior border of the optic chiasma. 



c. The Oculo-motor or III. cranial nerves arise in 

 the space between the' two crura cerebri. 



d. The Patheticus or IV. cranial nerve is very 

 small, and on the ventral surface appears in the space 

 between the cerebral hemisphere and the crus cerebi 

 on each side. The real origin is from the valve of 

 Vieussens on the dorsal side of the brain. It may be 

 followed back easily to this point. 



e. The Trigeminal or V. cranial nerve is very 

 large, and arises from the sides of the pons by two 

 roots. The smaller, inner one is the motor root ; the 

 larger, outer one the sensory root. 



f. The Abducens or VI. cranial nerve is small, and 



